What needle type and size are you using? What thread are you using? Stitch length?
Is the quilt level with the bed of the sewing machine? . You mentioned that it works on the smaller sample size but the issues happen when working on the actual quilt .It sounds like you are getting drag on the quilt.
What speed are you using to quilt? If you can, slow the machine speed button.
Try a Topstitch needle in the 9/14 size.
Is the quilt level with the bed of the sewing machine?